1. Field of the Invention
The present invention relates to fiber optic connectors and more particularly to a fiber optic coupling system for optically coupling together two fiber optic cables, which may or may not have different core diameters, to enable signal light to be transmitted between the two fiber optic cables with a minimum of signal light loss.
2. Description of the Prior Art
In long distance telecommunications systems and other signalling systems, more and more use is being made of fiber optic cables, or light guides, in the transmission of modulated light signals between distant locations due to the comparatively low attenuation inherent in fiber optic cables. However, in such long distance signalling systems utilizing fiber optic cables, connection obviously must be made from cable to cable and from cables to repeaters, light signal transmitters and other electro-optical devices.
Fiber optic connectors are therefore needed to produce such connections. However, it is necessary that a fiber optic connector properly align the abutting optical fibers in any two fiber optic cables to be optically coupled together. This is due to the fact that any lateral misalignment between abutting optical fibers of the cables to be optically coupled together can produce a significant attenuation of any light signals transmitted therebetween.
Various types of fiber optic connectors or couplers have been proposed to minimize the loss or attention of light signals when optically coupling two fiber optic cables or light guides together.
In a first type of fiber optic connector, the ends of two fiber optic cables are respectively mounted within two plugs (or connectors). The ends of the fiber optic cables come into direct contact with each other to couple the fiber optic cables together when the plugs are connected together. This first type of fiber optic connector requires a high degree of precision alignment in the centering of the two mating plugs with respect to each other to minimize light signal loss between the two fiber optic cables.
A second type of fiber optic connector, disclosed in U.S. Pat. No. 4,420,219, avoids the critical alignment problem involved in the above-discussed first optic connector by coupling first and second light guides to each other by way of a pair of lenses respectively mounted in a pair of mating plugs, which plugs house the first and second light guides. More specifically, in this second type of fiber optic connector a converging aspheric plano convex lens, having an aspherically shaped surface and a flat surface, is fastened in each of two plugs to be connected together. The flat surfaces of the lenses face outwardly so that they are in an abutting relationship with respect to each other when the plugs are connected together. The two light guides to be optically coupled together are also respectively fastened in the associated plugs, with the end surfaces of the light guides facing the associated aspherically shaped surfaces of the lenses and being substantially positioned at the respective focal points of the lenses. As a result, when the two plugs are connected together, light signals can be transmitted from the first light guide to the second light guide by way of the two abutting aspheric plano convex lenses.
Since the light guides are respectively fastened inside of the associated mating plugs and the end surfaces of the light guides are substantially positioned at the respective focal points of the associated lenses, this second type of fiber optic connector is limited in operation to only one particular size of light guide in each associated plug.
A third type of fiber optic connector, disclosed in U.S. Pat. No. 4,294,511, is basically a variation of the second type discussed above. In this third type of fiber optic connector a lens system is positioned between first and second light guides. This lens system, similar to that of U.S. Pat. No. 4,420,219, includes first and second lenses, each having a planor or flat surface and a convex surface. However, the flat surfaces of the lenses respectively face the ends of the first and second light guides, while the convex surfaces of the lenses face each other. The ends of the first and second light guides are substantially positioned at the focal points of the respective first and second lenses to enable light signals to be transmitted from the first light guide to the second light guide by way of the lens system.
The background art known to applicants at the time of the filing of this application is as follows:
U.S. Pat. No. 4,294,511, Connecting Optical System For Light Guides, by N. Yamashita et al.; and
U.S. Pat. No. 4,420,219, Optical Waveguide Connector Using Aspheric Lenses, by F. Muchel.
None of the above-described different types of fiber optic connectors teaches or suggests a fiber optic coupling system which not only avoids the critical alignment problem involved in the abovediscussed first optic connector but also has the adaptability to optically couple together two fiber optic cables or light guides having either different or similar core diameters.